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MS Visual Basic 6

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MS Visual Basic 6

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  1. MS Visual Basic 6 Walter Milner

  2. VB 6 • 0 Introduction • background to VB, A hello World program • 1 Core language 1 • Projects, data types, variables, forms, controls , a calculator program • 2 Core language 2 • Conditional statements, exception handling, loops, arrays, debugging • 3 Core language 3 • Functions, sub-routines, parameter passing, modules, scope, lifetime • 4 Controls • scrollbar, radio buttons, checkboxes, listboxes, timers, control arrays • 5 Graphics • primitives and image files • 6 Forms • Forms MDI, menus • 7 Files and databases • adding controls, using data files, using databases • 8 Deployment

  3. Hello World in VB • Start VB • New Project – Standard .exe • Click the Button control on the ToolBox and drag in the form • Double click the new button to invoke the code editor • Enter code: • Click the Run button Private Sub Command1_Click() MsgBox ("Hello world") End Sub Exercise – try this out

  4. What is Visual Basic? • Kemeny and Kurtz – Dartmouth College 1964 • For students – simple interpreted • Many versions since • MS VB versions – more power not so simple • VBScript VBA .NET framework • RAD especially of user interface

  5. A very early version

  6. VB is not.. • Vendor independent • Platform independent • Based on a constant language definition • Separated definition and IDE implementation • Well documented • (IMO) suitable for very large projects which must be maintained over a long period of time

  7. VB is .. • easy to use • suitable for RAD • very marketable

  8. Building an application - steps • Commercial – data driven – waterfall model – project management • Science/engineering – underlying data and physical model, algorithms, testing • In VB – RAD – focus on user interface prototyping and review.

  9. Building an application - forms • VB uses 'form' to mean Window • Info on form stored in a .frm file • VB system draws form based on that info • Forms can be treated like classes in OOP - later

  10. Building an application - controls • Buttons, text boxes, labels, check boxes.. • VB 'control' = user interface widget • Some invisible – timer • Controls have properties eg background color • Three kinds – • standard • non-standard MS controls (common dialog, tab) and 3rd party • ActiveX controls written in-house

  11. Building an application - modularity • Spaghetti programming, structured programming, OOP = increasing modularity • In VB application constructed from modules = files in project- • Form modules • BASIC modules • Class modules • Private and public control interaction between modules

  12. Building an application - objects • Some OOP in VB – not pure OOP • objects = things eg a form • class = type of object eg a form design • property = data value associated with object • method = something the object can do

  13. Building an application – example of OOP Form2 is a class f is an object – an instance of class Form2 Dim f As Form2 Set f = New Form2 f.Show f.BackColor = RGB(255, 0, 0) the Form2 class has a method called show It has a property called BackColor

  14. Event-driven programming • Standard approach for GUIs • Contrast with old character interfaces – program determines what happens • In GUI, the user triggers what application does (mostly) • Event examples are key press, mouse move, timer timeouts • Correspond to native Windows Messages (next slide) • Event handler = a subroutine which will execute when that event happens

  15. Windows Messages – Spy++